2 The potential for fisheries-induced adaptive changesErnande et al.Bruno Ernande, NMA Course, BergenThe potential for fisheries-induced adaptive changesThe commercial exploitation of fish stocks may not only have demographic consequences on the target species, but may also induce adaptive changes in their life history because fishing is by essence selective (Stokes et al. 1993, Palumbi 2001, Ashley et al ).Adaptive changes can have two different origins (Rijnsdorp 1993, Law 2000):Phenotypic plasticity: most species can modify their phenotype in the short term in response to environmental variation;Evolution: the prerequisites for contemporary fisheries-induced evolution are met:Fisheries selective pressure is strong: fishing mortality on average 2 to 3 times higher than natural mortality (Law 2000)most life history traits have sufficient heritability to evolve and micro-evolutionary changes have been proven to occur within a few generations in controlled and field experiments (Reznick et al. 1990; Conover & Munch 2002)Phenotypic plasticity and evolution have very different implications for management purposes: plasticity can be reversed within a generation whereas to mitigate adverse evolutionary changes requires many such generations.

3 Phenotypic plasticity or evolutionErnande et al.Bruno Ernande, NMA Course, BergenPhenotypic plasticity or evolutionWith empirical data, one has to disentangle plastic and evolutionary response. Evolutionary changes in life history traits can be assessed by modifications in their reaction norms.PlasticchangePhenotypeEnvironment

4 Phenotypic plasticity or evolutionErnande et al.Bruno Ernande, NMA Course, BergenPhenotypic plasticity or evolutionWith empirical data, one has to disentangle plastic and evolutionary response. Evolutionary changes in life history traits can be assessed by modifications in their reaction norms.EvolutionarychangePhenotypeEnvironment

5 Ernande et al.Bruno Ernande, NMA Course, BergenObjectivesModifications of reaction norms have been recently shown for age and size at maturation in commercially exploited fish stocks, e.g., North East Artic cod (Heino et al. 2002), North Sea plaice (Grift et al. 2003), Georges Bank cod (Barot et al. 2003), and Nothern cod (Olsen et al. 2003).We propose a theoretical approach for modelling the evolution of maturation reaction norms in exploited populations in order to tackle three specific points:Can harvesting be really responsible for evolutionary changes in maturation reaction norms?Can we evaluate the evolutionary impact of different harvesting practices and the potentiality of different management policies?What are the consequences of evolutionary changes on population abundance and sustainability?Ernande et al Proc Roy Soc B

17 Control of the sensitivity of the evolutionary responseErnande et al.Bruno Ernande, NMA Course, BergenControl of the sensitivity of the evolutionary responseThe sensitivity of the evolutionary response of maturation reaction norms to harvesting is controlled by three life history parameters: it increases asthe average natural mortality rate decreases,the average growth rate increases,the strength of the trade-off between growth and reproduction weakens.Sensitivitynatural moralitygrowth ratetrade-off strengthErnande et al Proc Roy Soc B

19 Consequences for population sustainabilityErnande et al.Bruno Ernande, NMA Course, BergenConsequences for population sustainabilityThe previous insights are qualitatively the same for the three management policies.The main difference between the three management policies lies in the consequences of evolutionary changes of the maturation reaction norm on population abundance.

22 Ernande et al.Bruno Ernande, NMA Course, BergenConclusionsFishing can induce evolutionary modifications in the position and the shape of the maturation reaction norm.The direction of these changes actually depends on the life history stage which is harvested when harvesting depends on maturity statusAccording to the sensitivity analysis, these changes could be minimized by fishing mainly adults and by focusing on species characterized by high natural mortality, low growth rate, and a strong trade-off between growth and reproduction.The prevalent system of management currently, quotas, seems to be the worse management practice in terms of fisheries-induced evolutionThe consequences of these evolutionary changes on stock abundance and sustainability may be dramatic as suggested by the example of extinction through evolutionary suicide. Simple population dynamics models would overlook this possibility, which highlights the necessity to take evolutionary trends into account in responsible management practices.